JP5487676B2 - Electrochemical device comprising an active material, an electrode including the active material, and an electrolyte solution including the electrode and a lithium salt - Google Patents

Description

The present invention is an active material, the electrode containing the same, the electrochemical device relates to comprises an electrolyte solution containing the electrodes and a lithium salt.

As a substitute material for LiCoO ₂ which is a positive electrode material of a lithium ion secondary battery, LiNiO ₂ , a composite oxide obtained by substituting Ni of LiNiO ₂ with another metal element, and the like have attracted attention. _However, LiNiO ₂ based materials such composite oxides obtained by substituting Ni of LiNiO 2, LiNiO ₂ with other metal elements are known to be highly hygroscopic.

Patent Document _1, a manufacturing method of LiNiO ₂ based materials such as LiNiO 2, composite oxides of Ni LiNiO ₂ was replaced by another metal element is disclosed, and in particular, below 800ppm the water content of LiNiO ₂ materials It is described that gas generation during use can be suppressed by doing so. As a reason for this, according to Patent Document 1, when the amount of water in the LiNiO ₂ -based material is large, the amount of water adsorbed on the surface of the LiNiO ₂ -based material increases, and at least a part of this water is electrolyzed during charging and gas Is disclosed.

JP 2003-17054 A

However, there is still room for improvement in the discharge capacity of the LiNiO ₂ -based material.

The present invention is to provide a high discharge capacity, an active material mainly composed of lithium composite oxide containing nickel, the electrodes containing the same, the electrochemical device comprising an electrolyte solution containing the electrodes and a lithium salt, a With the goal.

The active material according to the present invention is mainly composed of a composite oxide represented by the following formula (1), and has a water content of 200 to 350 mass ppm.
LiNi _x M _1-x O ₂ (1)
In formula (1), x satisfies 0.5 ≦ x <1, and M is one or more arbitrary metal elements.

  The electrode according to the present invention includes a current collector and an active material layer including the active material and provided on the current collector.

  Moreover, the electrochemical device according to the present invention includes an electrolyte solution containing the electrode and a lithium salt.

  When the water content (water content) contained in the active material containing the composite oxide represented by the formula (1) as a main component is a value within the range of 200 to 350 ppm by mass, It has been found that the discharge capacity of an electrochemical device comprising an electrode containing a substance and an electrolyte solution containing a lithium salt is significantly improved. The reason is not necessarily clear, but the active material mainly composed of the composite oxide represented by the above formula (1) is considered to hold most of the specific amount of water molecules in the crystal lattice. Intercalation / deintercalation of Li ions into the active material during charging / discharging causes expansion and contraction to the crystal lattice of the active material, but the presence of water molecules in the crystal lattice It is considered that deformation of the active material accompanying expansion and contraction is suppressed, and Li ion intercalation / deintercalation is easily performed. If the amount of water is too large, the amount of water molecules adsorbed on the surface of the active material increases, and side reactions between the water and the organic electrolyte (for example, decomposition reaction of the organic electrolyte) increase. Thus, if the amount of water is too small, the number of water molecules held in the crystal lattice will decrease, and it will be difficult to sufficiently improve the discharge capacity.

Here, the active material and water content according to the present invention are preferably 233 to 297 mass ppm.

Moreover, the manufacturing method of the lithium ion secondary battery which concerns on this invention includes the water adjustment process which makes the water content of the active material which has a complex oxide represented by following formula (1) a main component 200-350 mass ppm. Prepare.
LiNi _x M _1-x O ₂ (1)
In formula (1), x satisfies 0.5 ≦ x <1, and M is an arbitrary metal element.

  Thereby, the active material which concerns on this invention mentioned above can be obtained.

According to the present invention, there is provided a high discharge capacity, an active material mainly composed of lithium composite oxide containing nickel, the electrodes containing the same, the electrochemical device comprising an electrolyte solution containing the electrodes and a lithium salt, a be able to.

FIG. 1 is a schematic cross-sectional view of a lithium ion secondary battery according to this embodiment. FIG. 2 is a graph plotting the horizontal axis as the water content (ppm) of the active material and the vertical axis as the discharge capacity (mAh / g) of the evaluation cell in Examples 1 to 10 and Comparative Examples 1 to 4.

  Hereinafter, preferred embodiments of the present invention will be described in detail. Note that the dimensional ratios of the drawings to be referred to do not necessarily match the actual dimensional ratios.

<Active material>
The active material according to the present embodiment has a water content of 200 to 350 mass ppm and contains a composite oxide represented by the following formula (1) as a main component.
LiNi _x M _1-x O ₂ (1)
In formula (1), x satisfies 0.5 ≦ x <1, and M is one or more arbitrary metal elements.

  In the formula (1), x is preferably 0.7 to 0.9 from the viewpoint of further improving the discharge capacity.

  In formula (1), M is preferably one or more metal elements selected from the group consisting of Co, Mn, and Al. Moreover, when M is 1 type, it is preferable that M is Co, and when it is 2 types, the combination of Co and Al (molar ratio 3: 1), the combination of Co and Mn (molar ratio 1). 1).

  In the present invention, “having the composite oxide represented by formula (1) as a main component” means that the amount of the composite oxide represented by formula (1) in the active material is 90% or more on a mass basis, Preferably it means 95% or more.

The water content (water content) contained in the active material is 200 to 350 ppm by mass, and is preferably 233 to 297 ppm by mass from the viewpoint of significantly increasing the discharge capacity. The water content can be measured by the Karl Fischer method.

  The shape of the active material is not particularly limited, but when producing an electrode, from the viewpoint of the conductive material mixed with the active material, the affinity with the binder, and the good applicability of the mixture to the current collector, It is preferably in the form of particles. From the viewpoint of improving the contact area with the electrolytic solution, the primary particle diameter (D10) with a cumulative ratio of 10% is 1 to 10 μm, the primary particle diameter (D50) with a cumulative ratio of 50% is 11 to 20 μm, The primary particle diameter (D90) having a cumulative ratio of 90% is preferably 21 to 30 μm, more preferably D10 is 5 to 8 μm, D50 is 12 to 16 μm, and D90 is 22 to 26 μm. D10, D50, and D90 can be obtained based on the volume-based particle size distribution obtained for the active material by a known laser diffraction / scattering particle size distribution measuring apparatus.

<Method for producing active material>
Examples of the raw material compound of the composite oxide represented by the formula (1) include the following compounds.
As the lithium source, that is, the compound containing lithium element, various lithium compounds such as Li ₂ CO ₃ , LiNO ₃ , LiOH, LiOH · H ₂ O, organolithium compounds such as alkyl lithium and lithium acetate, LiCl, Various lithium compounds such as lithium halides such as LiI can be mentioned.
Examples of the nickel source, that is, the compound containing nickel element include Ni (OH) ₂ , NiO, NiOOH, NiCO ₃ .2Ni (OH) ₂ .4H ₂ O, Ni (NO ₃ ) ₂ .6H ₂ O, NiSO _4. , NiSO ₄ .6H ₂ O, organic nickel compounds such as fatty acid nickel and nickel oxalate, and various nickel compounds such as nickel halides.
Examples of the compound containing M (metal element), that is, a compound containing M (metal element) include the following compounds.
When M is manganese, manganese sources include Mn ₃ O ₄ , Mn ₂ O ₃ , MnO ₂ , MnOOH, MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , an organic manganese compound, manganese hydroxide, and Various manganese compounds such as manganese halides can be mentioned.
When M is cobalt, cobalt sources include Co (OH) ₂ , CoO, Co ₂ O ₃ , Co ₃ O ₄ , organic cobalt compounds such as cobalt acetate, CoCl ₂ , Co (NO ₃ ) ₂ .6H _2. Examples include various cobalt compounds such as O and Co (SO ₄ ) · 7H ₂ O.
When M is aluminum, the aluminum _{source, AlOOH, Al 2 O 3,} Al (OH) 3, AlCl 3, Al (NO 3) 3 · 9H 2 O, the organic aluminum compound and _Al 2 _{(SO 4) 3} And various aluminum compounds.

  These raw material compounds are mixed with, for example, a ball mill, and the mixture is fired to obtain a composite oxide having a desired composition. Here, the firing conditions of the mixture are not particularly limited. For example, the firing may be performed in an oxygen-containing gas atmosphere at a temperature of 700 to 1050 ° C. for 0.5 to 50 hours. As the baking apparatus, a conventional apparatus may be used. For example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln, or the like can be used.

  Next, in order to remove impurities from the fired composite oxide, the obtained composite oxide is washed with a cleaning liquid such as water. For example, the obtained composite oxide and distilled water may be sufficiently stirred in a container, and then the composite oxide may be recovered by filtration or the like. The cleaning conditions are not particularly limited. Here, the impurities are, for example, raw material compounds that have not contributed to the formation of the composite oxide.

  Next, the composite oxide recovered from the cleaning liquid after the cleaning is dried. At this time, the water content (water content) contained in the active material is set to 200 to 350 mass ppm. The drying method is not particularly limited, and examples thereof include heating, evacuation, and leaving in an atmosphere having a predetermined moisture content. The drying conditions are not particularly limited, and can be appropriately set according to the amount of water contained in the active material before drying and the drying method to be applied. For example, drying combined with heating and evacuation is preferable because the amount of moisture can be adjusted in a relatively short time. Specifically, as the drying method, for example, first, the composite oxide is washed with water, or water is added to the composite oxide, and then preliminarily stored in a constant temperature bath having an air atmosphere of about 70 to 100 ° C. Dry. Then, the method of performing this drying at about 70-100 degreeC, evacuating is mentioned. By appropriately adjusting the temperature and time of the preliminary drying and the temperature and time of the main drying, the amount of water contained in the active material after drying can be set in the range of 200 to 350 mass ppm. In addition, substitution drying with ethyl alcohol or isopropyl alcohol may be performed before the preliminary drying. The preliminary drying may be performed in an inert gas atmosphere such as nitrogen.

  Also, depending on the cleaning method, such as when using a cleaning liquid other than water, the water content of the active material before moisture adjustment may be less than 200 to 350 ppm by mass. The moisture content may be adjusted to the above range by humidifying the active material, for example, by leaving it in an atmosphere.

<Positive electrode (electrode)>
Next, the positive electrode (electrode) 10 according to the present embodiment will be described with reference to FIG.

  The positive electrode 10 according to the present embodiment includes a current collector 12 and a positive electrode active material layer 14 that is provided on the current collector 12 including the active material whose water content is adjusted as described above.

  As the current collector 12 of the positive electrode 10, for example, a metal foil such as an aluminum foil can be used. The positive electrode active material layer 14 provided on the current collector 12 is a layer containing the above-described active material, binder, and a conductive material in an amount necessary.

  The binder is not particularly limited as long as the active material and the conductive material can be bound to the current collector, and a known binder can be used. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoro Fluorine such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene copolymer Resin. This binder not only binds constituent materials such as active materials and conductive materials, but also contributes to binding between the constituent materials and the current collector. In addition to the above, for example, polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, cellulose, styrene / butadiene rubber, isoprene rubber, butadiene rubber, ethylene / propylene rubber, and the like may be used as the binder. Also, thermoplastic elastomeric polymers such as styrene / butadiene / styrene block copolymers, hydrogenated products thereof, styrene / ethylene / butadiene / styrene copolymers, styrene / isoprene / styrene block copolymers, and hydrogenated products thereof. May be used. Further, syndiotactic 1,2-polybutadiene, ethylene / vinyl acetate copolymer, propylene / α-olefin (carbon number 2 to 12) copolymer and the like may be used. Further, a conductive polymer may be used.

  The conductive material is not particularly limited, and a known conductive material can be used. Examples thereof include carbon blacks, carbon materials, metal powders such as copper, nickel, stainless steel, and iron, mixtures of carbon materials and metal powders, and conductive oxides such as ITO.

<Method for producing positive electrode>
The positive electrode 10 described above includes, for example, the above-described active material, binder, and a conductive material in an amount necessary, and a solvent corresponding to the type thereof, such as N-methyl-2-pyrrolidone in the case of PVDF, N, The slurry can be prepared by adding to a solvent such as N-dimethylformamide, and the slurry is applied to the surface of the current collector 12 and dried.

  The above step is preferably performed in a dry room having a dew point of −40 ° C. or lower in order to maintain the water content of the active material at 200 to 350 mass ppm.

<Lithium ion secondary battery>
Next, a lithium ion secondary battery including the electrode including the active material described above will be briefly described with reference to FIG.

  The lithium ion secondary battery 100 mainly includes a stacked body 30, an exterior body 50 that accommodates the stacked body 30 in a sealed state, and a pair of leads 60 and 62 connected to the stacked body 30.

  The laminated body 30 is configured such that a pair of the positive electrode 10 and the negative electrode 20 are opposed to each other with the separator 18 interposed therebetween. The positive electrode 10 is as described above. The negative electrode 20 is a product in which a negative electrode active material layer 24 is provided on a negative electrode current collector 22. The positive electrode active material layer 14 and the negative electrode active material layer 24 are in contact with both sides of the separator 18. Leads 60 and 62 are connected to the end portions of the positive electrode current collector 12 and the negative electrode current collector 22, respectively, and the end portions of the leads 60 and 62 extend to the outside of the exterior body 50.

  As the negative electrode current collector 22, a copper foil or the like can be used. Moreover, as the negative electrode active material layer 24, the thing containing a negative electrode active material, a binder, and the quantity of electrically conductive material as needed can be used. As the binder and the conductive material, those exemplified for the positive electrode can be used.

Examples of the negative electrode active material include graphite, non-graphitizable carbon, graphitizable carbon, and low-temperature calcined carbon that can occlude / release (intercalate / deintercalate, or dope / dedope) lithium ions. Carbon materials, metals that can be combined with lithium such as Al, Si and Sn, amorphous compounds mainly composed of oxides such as SiO ₂ and SnO ₂ , lithium titanate (Li ₄ Ti ₅ O ₁₂ ), etc. The particle | grains containing are mentioned.

  The manufacturing method of the negative electrode 20 should just adjust slurry and apply | coat to a collector like the manufacturing method of the positive electrode 10. FIG.

The electrolyte solution is contained in the positive electrode active material layer 14, the negative electrode active material layer 24, and the separator 18. The electrolyte solution is not particularly limited. For example, in the present embodiment, an electrolyte solution containing a lithium salt (electrolyte aqueous solution, electrolyte solution using an organic solvent) can be used. However, the electrolyte aqueous solution is preferably an electrolyte solution (non-aqueous electrolyte solution) using an organic solvent because the electrochemical decomposition voltage is low, and the withstand voltage during charging is limited to a low level. As the electrolyte solution, a lithium salt dissolved in a non-aqueous solvent (organic solvent) is preferably used. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ , CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , Salts such as LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ , LiBOB (lithium bis (oxalate) borate) Can be used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together.

  Moreover, as an organic solvent, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate etc. are mentioned preferably, for example. These may be used alone or in combination of two or more at any ratio.

  In the present embodiment, the electrolyte solution may be a gel electrolyte obtained by adding a gelling agent in addition to liquid. Further, instead of the electrolyte solution, a solid electrolyte (a solid polymer electrolyte or an electrolyte made of an ion conductive inorganic material) may be contained.

  The separator 18 may also be formed of an electrically insulating porous structure, for example, a single layer of a film made of polyethylene, polypropylene or polyolefin, a stretched film of a laminate or a mixture of the above resins, or cellulose. And a fiber nonwoven fabric made of at least one constituent material selected from the group consisting of polyester and polypropylene.

  The exterior body 50 seals the laminated body 30 and the electrolytic solution therein. The outer package 50 is not particularly limited as long as it can prevent leakage of the electrolytic solution to the outside and entry of moisture and the like into the lithium ion secondary battery 100 from the outside. For example, as the outer package 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil 52, and a film such as polypropylene can be used as the synthetic resin film 54. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is preferably polyethylene or polypropylene.

  The leads 60 and 62 are made of a conductive material such as aluminum.

<Method for producing lithium ion secondary battery>
Then, the manufacturing method of the lithium ion secondary battery which concerns on this embodiment is demonstrated. The manufacturing method of the lithium ion secondary battery according to the present embodiment includes a positive electrode 10 containing the active material, a negative electrode 20, a separator 18 interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte solution containing a lithium salt. And a step of enclosing the outer body 50 in the exterior body 50.

  For example, the positive electrode 10 containing the active material described above, the negative electrode 20 and the separator 18 are stacked, and the positive electrode 10 and the negative electrode 20 are heated and pressed with a press tool from a direction perpendicular to the stacking direction. 10, the separator 18 and the negative electrode 20 are brought into close contact with each other. Then, for example, a lithium ion secondary battery can be manufactured by placing the laminate 30 in a bag-shaped outer package 50 prepared in advance and injecting a non-aqueous electrolyte solution containing the lithium salt. Instead of injecting the non-aqueous electrolyte solution containing the lithium salt into the outer package, the laminate 30 may be impregnated in advance with the non-aqueous electrolyte solution containing the lithium salt.

  The above step is preferably performed in a dry room having a dew point of −40 ° C. or lower in order to maintain the water content of the active material in the positive electrode 10 at 200 to 350 mass ppm.

According to this embodiment, the water content of the active material of the positive electrode 10 is 200 to 350 mass ppm, and this active material is mainly composed of the composite oxide represented by the formula (1). A lithium ion secondary battery containing such an active material has an extremely high discharge capacity compared to the conventional one. The reason is not necessarily clear, but the active material mainly composed of the composite oxide represented by the formula (1) is considered to hold most of the specific amount of water molecules in the crystal lattice. And it is thought that the intercalation of Li ions into the active material during discharge is facilitated due to the presence of water molecules. If the amount of water contained in the active material is too large, the amount of water molecules adsorbed on the surface of the active material will increase, and the reaction between the water and the organic electrolyte will increase, and the amount of water will be too small. In this case, water molecules held in the crystal lattice are reduced, and it is considered that none of them can sufficiently improve the discharge capacity. Moreover, since such an active material does not contain much Co like LiCoO ₂ , a lithium ion secondary battery can be obtained at a lower cost than in the past.

  As described above, the preferred embodiment of the active material, the electrode including the active material, the lithium ion secondary battery including the electrode, and the method of manufacturing the lithium ion secondary battery including the electrode has been described in detail. It is not limited to the embodiment.

  For example, the active material according to the present embodiment can be used as an electrode material for electrochemical elements other than lithium ion secondary batteries. As such an electrochemical element, a secondary battery other than a lithium ion secondary battery, such as a metallic lithium secondary battery (using the electrode containing the active material of the present invention for the cathode and metallic lithium for the anode). And an electrochemical capacitor such as a lithium capacitor provided with an electrolyte solution containing a lithium salt. These electrochemical elements can be used for power sources such as self-propelled micromachines and IC cards, and distributed power sources arranged on or in a printed circuit board.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
<Production of active material>
LiOH.H ₂ O, Ni (OH) ₂ , Co (OH) ₂ , and AlOOH become Li: Ni: Co: Al = 1.05: 0.8: 0.15: 0.05 (atomic ratio). And mixed with a ball mill. This mixture was fired at 850 ° C. for 10 hours in an air atmosphere to obtain a fired product of LiNi _0.8 Co _0.15 Al _0.05 O ₂ . And after completion | finish of baking, the obtained complex oxide was grind | pulverized.

(Composite oxide cleaning process)
Thereafter, 70 g of the obtained composite oxide and 600 ml of distilled water were placed in a 1,000 ml beaker, stirred for 15 minutes with a stirrer, transferred to a suction filter, dehydrated in 60 minutes, and the composite oxide was washed. It was.

(Drying process of complex oxide)
Next, the composite oxide remaining on the filter paper is placed in a thermostat kept at 90 ° C., preliminarily dried for 24 hours, and then evacuated in the thermostat (steady pressure after start of evacuation: 13.33 kPa). ), This drying was performed at 80 ° C. for 48 hours to obtain an active material of Example 1. When the amount of water (water content) remaining in the active material was measured by a coulometric titration method in the Karl Fischer method, it was 309 mass ppm.

<Measurement of discharge capacity>
A mixture of the active material of Example 1, polyvinylidene fluoride (PVDF) as a binder, and acetylene black was dispersed in N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a slurry. The slurry was prepared so that the weight ratio of the active material, acetylene black, and PVDF was 90: 5: 5 in the slurry. This slurry was applied onto an aluminum foil as a current collector, dried, and then rolled to obtain an electrode (positive electrode) on which an active material layer containing the active material of Example 1 was formed.

Next, the obtained electrode and the Li foil as the counter electrode were laminated with a separator made of a polyethylene microporous film interposed therebetween to obtain a laminate (element body). This laminate was put in an aluminum laminator pack, and 1M LiPF ₆ solution was injected as an electrolyte into the aluminum laminate pack, followed by vacuum sealing to produce an evaluation cell of Example 1.

  Using the evaluation cell of Example 1, the discharge capacity (unit: mAh / unit) when the discharge rate is 0.1 C (current value at which discharge is completed in 10 hours when constant current discharge is performed at 25 ° C.) g) was measured. The discharge capacity at 0.1 C was 196 mAh / g.

(Examples 2 to 10, Comparative Examples 1 to 4)
About the drying in a thermostat, the active material of Examples 2-10 and Comparative Examples 1-4 was carried out similarly to Example 1 except having changed the preliminary drying conditions and this drying conditions as shown in Table 1 below. Got. Table 1 shows the amount of moisture remaining in the active material (water content) and the discharge capacity of the evaluation cell using these active materials.

FIG. 2 is a graph in which the horizontal axis represents the water content (ppm) of the active material and the vertical axis represents the discharge capacity (mAh / g) of the evaluation cell. All of the active materials of Examples 1 to 10 in which the water content of the active material was in the range of 200 to 350 ppm by mass had a discharge capacity larger than 190 mAh / g (threshold A). Moreover, as for the active material of Examples 2, 3, 4, 6, and 8 whose water content of an active material exists in the range of 233-297 mass ppm, all have discharge capacity larger than 200 mAh / g (threshold B), An extremely high discharge capacity was obtained.

  As mentioned above, according to the lithium ion secondary battery provided with the electrode containing the active material of this invention, a high discharge capacity can be obtained.

Claims (4)

An active material having as a main component a composite oxide represented by the following formula (1) in which water molecules are present in a crystal lattice and having a water content of 200 to 350 ppm by mass.
LiNi _x M _1-x O ₂ (1)
[In the formula (1), x satisfies 0.5 ≦ x <1, and M is one or more arbitrary metal elements. The active material according to claim 1, wherein the water content is 233 to 297 mass ppm. An electrode comprising a current collector and an active material layer comprising the active material according to claim 1 and provided on the current collector An electrochemical device comprising an electrolyte solution comprising the electrode according to claim 3 and a lithium salt.

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